: Nearly two million essentially non speaking individuals today rely on speech output devices to communicate needs and desires, and to assist in meeting independence, health, and social/emotional needs. Despite the increased use of speech output devices research and theoretical analysis of the cognitive processes associated with the coding schemes used to retrieve stored vocabulary items are nearly non existent. The broad aims in this project are to provide fundamental empirical information, to construct and evaluate a formal model of the learning process involved in acquiring the coding scheme and to develop a theoretical framework on the cognitive processes associated with widely used coding schemes. Specific objectives include investigation of three components: (1) acquisition of the coding scheme; (2) the retention of the coding scheme; and this project is the investigation of these three components as a function of variations un user characteristics (e.g., congenital disabling conditions, mentally retarded, and normals with varying levels of working memory), criterial task demands, vocabulary, and coding scheme characteristics. In a series of five experiments, the coding scheme, the nature of the vocabulary, user characteristic, training procedures, and retention interval will be systematically manipulated. The influences of these experiments test predictions from an adaptive network model developed to stimulate the learning process. Some of these experiments also test the assumption guiding this project that each coding scheme will have unique advantages and disadvantages depending on the task demands and the user characteristics. This research will have broad-based significance for current training and utilization of speech prosthesis devices.